Electronic control for a hydraulically driven generator

ABSTRACT

Electronic control for a hydraulic system driving an auxiliary power source is provided, with specific application as a system for controlling the operation of a hydraulically driven AC generator. The system may includes a hydraulic pump, a hydraulic motor drivably connected to the generator, a fluid circuit for circulating fluid from the pump to the motor and back. The fluid circuit may contain a bypass conduit to bypass the motor. The system also includes a proportional servo control valve assembly for controlling the fluid circuits and a control circuit for controlling the proportional control valve assembly. The control system can be capable of controlling the flow of hydraulic fluid to the motor powering the electrical or mechanical system. Sensors for measuring the operating parameters of the system and an operator interface module can influence the operation of the system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to an electronic control for hydraulicsystem, and more particularly to precision control of hydraulicallydriven generators for stabilizing frequency and voltage outputcharacteristics.

2. Background Art

Most engine driven vehicles utilize an internal combustion engine as theprimary power source for propelling a vehicle. However, numerous modulesand devices for the vehicle as well as the engine require electricalpower. Typically, a rechargeable battery is provided with the vehicle asa basic power supply. The battery power supply system provides directcurrent (DC) electrical power for starting the vehicle engine and foroperating certain DC compatible electrical loads when the vehicle is notrunning. The battery is recharged to maintain power by an alternatorcoupled to and driven by the engine when the vehicle is running.Concurrently, the alternator also provides DC electrical power to thevehicle electrical loads.

With the advent of electronics in today's modern vehicle, groundvehicles, boats and aircraft alike, the amount of electrical loads whichrequire power has significantly increased. Moreover, many variousauxiliary electrical loads are dependent upon stable alternating current(AC), for example, rescue and military vehicles having AC poweredcommunications equipment. Additionally, many other vehicles, such asutility and telephone company repair and maintenance vehicles andvehicles providing electrical welding equipment, are increasinglyutilizing AC equipment dependent upon clean AC power.

Various systems have been proposed for alleviating the complication ofoperating both AC and DC powered electrical equipment. One such systeminvolves driving an auxiliary AC generator from the vehicle's engine orprincipal power plant. This can be accomplished by connecting thegenerator to a power take off or to any other suitable connection toengine output. While this will indeed operate a generator, variations inengine speed will wreak havoc with characteristics of power output andtherefore with equipment which is dependent upon stable voltage andfrequency characteristics of electrical power.

Accordingly, various systems have been proposed to control speed of anAC generator. One such system utilizes a hydraulic circuit having aproportional valve for supplying a constant rate of fluid flow to ahydraulic motor. The hydraulic motor in turn drives a generator forsupplying AC power to certain AC compatible electrical loads. However,such systems can have difficulty maintaining precise frequency outputfor controlling the most sensitive AC equipment and are oftensusceptible to premature mechanical failure.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide ahydraulic control system for generating precise electrical outputcharacteristics, particularly frequency output, along with prolongingthe life of the system, thus reducing warranty returns and costsassociated therewith.

A hydraulic control system for driving an auxiliary power source,located aboard a motor vehicle having a primary power source, atconstant speed despite fluctuations in rotational speed of the primarypower source is provided. The system may include a hydraulic pump, ahydraulic motor, a fluid circuit, a proportional control valve assembly,and a control circuit. The hydraulic pump may be drivably connectable tothe primary power source and can have an inlet for receiving fluid forpumping and an outlet for discharging pumped fluid under pressure. Thehydraulic motor may be drivably connectable to the auxiliary powersource and can have an inlet for receiving fluid under pressure and anoutlet for discharging spent fluid. The fluid circuit may include asupply conduit for conducting fluid discharged by the pump to the motor,a return conduit for returning fluid discharged by the motor to thepump, and a bypass conduit for conducting fluid discharged by the pumpdirectly to the return conduit, bypassing the motor, and returning fluidto the pump.

The proportional control valve assembly can be disposed serially withrespect to the supply conduit and interposed between the outlet of thepump and the inlet of the motor. The control valve assembly may have ahousing including a valve chamber, a valve disposed within the valvechamber for apportioning the flow of fluid between the supply conduitand the bypass conduit, a solenoid drivably connectable to the valve forselectively moving the valve incrementally within the valve chamber froman open position to a closed position. Moreover, a first fluid passagemay be provided in fluid communication with the valve chamber and thesupply conduit going to the motor, while a second fluid passage may beprovided in fluid communication with the valve chamber and the bypassconduit. The valve can selectively close and open the first fluidpassage and the second fluid passage proportionally dividing the flow offluid therebetween.

The control circuit may be in electrical communication with the valveassembly for controlling the valve assembly and hence the fluid flowwithin the first fluid passage to the motor supply conduit and thesecond fluid passage to the bypass conduit. Further, the control circuitmay include a sensor electrically coupled to the auxiliary power sourcefor determining output frequency of the auxiliary power source. Areference signal generator for generating a reference signal indicativeof a predetermined output frequency may also be provided. Additionally,the control circuit can include a comparing subcircuit for comparingsensed output frequency with the reference signal, and for generating acontrol signal controlling the valve assembly such that the supply offluid conducted to the supply conduit be sufficient to maintain desiredoutput frequency.

Moreover, the control circuit of the hydraulic control system mayfurther include a temperature sensor disposed in the fluid circuit forsensing hydraulic fluid temperature. A system controller having a fluidpre-heating subcircuit may be provided for generating a control signalcontrolling the valve assembly such that fluid bypasses the hydraulicmotor entirely until safe fluid temperature is obtained. Further, thesystem controller may further include a power ramping subcircuit forgenerating a control signal controlling the valve assembly whensufficient fluid temperature is obtained such that power is suppliedgradually to the hydraulic motor.

Furthermore, the system controller may include an overtemperatureshutdown subcircuit for generating a control signal controlling thevalve assembly when fluid temperature becomes too hot for safe operationsuch that fluid bypasses the hydraulic motor, shutting down theauxiliary power source. Additionally, the control circuit can beequipped with an emergency override accessible by an operator forinstructing the system controller to continue system operation whenunsafe operating conditions exist.

It is another aspect of the present invention to provide a hydrauliccontrol system that senses fluid pressure in the fluid circuit andautomatically engages the auxiliary electrical system to power certainelectrical loads, provided safe operating temperatures are obtained.

Accordingly, the control circuit of the hydraulic control system mayfurther include a pressure sensor for determining sufficient hydraulicpressure for commencing system operation. The pressure sensor can causesystem operation to begin when hydraulic pressure is sufficient, andcan, correspondingly, cause system operation to shut down when hydraulicpressure is deficient.

Yet another aspect of the present invention is to control operation ofthe hydraulic circuit to perform under safe operating conditions.

Therefore, a method, according to the invention, for operating ahydraulic control system may include sensing hydraulic fluid temperaturein a fluid circuit, warming hydraulic fluid by circulating the fluidthrough portions of the fluid circuit bypassing a hydraulic motor, ifsensed fluid temperature is below safe operating temperature, andsupplying hydraulic fluid slowly through to the hydraulic motor oncehydraulic fluid reaches safe operating temperature to gradually bringthe motor up to desired speed so that full power operation can commence.

Warming the hydraulic fluid may involve maintaining open anelectronically controlled hydraulic proportional valve disposed withinthe fluid circuit such that fluid is directed entirely to a bypassconduit. Supplying hydraulic fluid slowly to the hydraulic motor mayinvolve gradually closing an electronically controlled hydraulicproportional valve disposed within the fluid circuit such that fluid isgradually conducted through a motor supply conduit in fluidcommunication with the hydraulic motor in order to gradually apply powerto the motor.

Moreover, the method for operating the hydraulic control system mayfurther include sensing hydraulic motor output characteristics andapportioning fluid flow to the hydraulic motor in order to maintainconstant motor output characteristics. Sensing hydraulic motor outputcharacteristics may involve sensing electrical output characteristics ofa generator driven by the hydraulic motor. Apportioning may involvecomparing sensed output characteristics with predetermined outputcharacteristics, generating a control signal based on the comparison,and selectively controlling an electronically controlled hydraulicproportional valve to move incrementally within a valve chamber suchthat fluid is proportionally divided between a motor supply conduit influid communication with the hydraulic motor and a bypass conduit, whichbypasses the hydraulic motor.

Further, the method of operating the hydraulic control system mayinclude preventing over-temperature damage to the hydraulic system whensensed fluid temperature exceeds safe operating temperature. Preventingover-temperature damage may involve annunciating the existence ofover-temperature conditions to an operator when a first high temperatureis obtained, triggering a timer to begin counting down a specified timewhen a second high temperature is obtained, and bypassing all fluid flowto the motor when the timer has expired. Bypassing all fluid flow to themotor can involve opening an electronically controlled hydraulicproportional valve disposed within the fluid circuit such that fluid isdirected entirely to a bypass conduit. Additionally, the method mayinclude overriding the bypassing step upon receipt of an emergencyoverride instruction from an operator to prevent shutdown and keep thesystem operating.

Furthermore, the method of operating the hydraulic control system mayalso include sensing fluid pressure in the fluid circuit, commencingoperation of an auxiliary power source if sensed fluid pressure issufficient by controlling a hydraulic proportional valve to meter fluidto the hydraulic motor, which drives the auxiliary power source, andceasing operation of an auxiliary power source if sensed fluid pressureis deficient by fully opening the proportional valve to bypass all fluidflow to the motor.

Still another aspect of the invention is to provide annunciation ofauxiliary power source output characteristics.

Still yet a further aspect of the invention is that acceleration of theauxiliary power source from the stopped condition, as well as coldtemperature condition, be gradual.

These and other aspects, objects, features and advantages of the presentinvention will become more clearly understood and appreciated from areview of the following detailed description of the preferredembodiments and appended claims, and by reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further object and advantages thereof, may best be understood withreference to the following description, taken in connection with theaccompanying drawings in which:

FIG. 1 is a schematic diagram of a hydraulic circuit exhibited in anexemplary control system according to an aspect of the presentinvention;

FIG. 2 is a schematic diagram of an alternate hydraulic circuitexhibited in an exemplary control system according to an aspect of thepresent invention;

FIG. 3 is a block diagram of a control circuit according to an aspect ofthe present invention; and

FIG. 4 is a graph generally displaying system characteristics duringcold start operation according to an aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

As required, detailed embodiments of the present invention are disclosedherein. However, it is to be understood that the disclosed embodimentsare merely exemplary of an invention that may be embodied in various andalternative forms. Therefore, specific functional details disclosedherein are not to be interpreted as limiting, but merely as arepresentative basis for the claims and/or as a representative basis forteaching one skilled in the art to variously employ the presentinvention.

A hydraulic control system 10, according to an aspect of the presentinvention, is illustrated in FIGS. 1 and 2. FIG. 1 generally depicts ahydraulic circuit 12 for the hydraulic control system 10, while FIG. 2generally depicts a control circuit 14 for the hydraulic control system10.

Referring first to FIG. 1, the hydraulic circuit 12 of the system 10 ispowered by a hydraulic pump 16, having an inlet 18 for receiving fluidfor pumping and an outlet 20 for discharging pumped fluid underpressure. The hydraulic pump 16 can be a variable displacement typepump, a fixed displacement type pump, or the like, for pumpingpressurized fluid throughout a fluid circuit 22. The hydraulic pump 16can be driven by a primary power source 24, such as a vehicle powertake-off (PTO), belt drive, gasoline engine, diesel engine, or anysimilar input. A hydraulic motor 26, having an inlet 28 for receivingfluid under pressure and an outlet 30 for discharging spent fluid, canbe disposed within the hydraulic circuit 12, as shown. The hydraulicmotor 26 drives an auxiliary power source 32, which provides electricalor mechanical power to vehicle loads or devices (not shown). Forexample, the auxiliary power source 32 can be an AC generator, amechanical drive system, or other source requiring constant rotationalspeed. The hydraulic motor 26 can be drivably connected to the auxiliarypower source 32 through a shaft 34 (as shown in FIGS. 1 and 2), or abelt or other means of power transmission (not illustrated). Moreover,the hydraulic motor 26 can be a fixed displacement gear type motor, vanetype motor, piston type motor, or the like.

The fluid circuit 22 can include a supply conduit 36, a return conduit38, and a bypass conduit 40. The supply conduit 36 can be divided intoat least two sections—a valve supply conduit 36 a and a motor supplyconduit 36 b. The supply conduit 36 conducts fluid discharged by thepump 16 to the motor 26, while the return conduit 38 returns fluiddischarged by the motor 26 to the pump 16. The bypass conduit 40,meanwhile, can be disposed in the fluid circuit 22 to conduct fluiddischarged by the pump 16 directly to the return conduit 38, bypassingthe motor 26, where the fluid is subsequently returned to the pump 16.

The system 10 preferably includes a proportional control valve assembly42, such as an electro-hydraulic servo control valve assembly,controlled by a system controller 44 (shown in FIG. 2). The proportionalcontrol valve assembly 42 can be disposed serially with respect to thesupply conduit 36 such that it is interposed between the outlet 20 ofthe pump and the inlet 28 of the motor. The control valve assembly 42may include a housing 46 generally enclosing a valve chamber 48. A valve50, which shuttles back and forth between an open position and a closedposition, may be disposed within the valve chamber 48. The control valveassembly 42 may further include a first fluid passage 52 and a secondfluid passage 54. Further, the control valve assembly 42 can be disposedwithin the hydraulic circuit 12 such that the first fluid passage 52 isin fluid communication with the valve chamber 48 and the motor supplyconduit 36 b, while the second fluid passage 54 is in fluidcommunication with the valve chamber 48 and the bypass conduit 40. Asolenoid 56 or other electronic or electromechanical device can bedrivably connected to the valve 50 for selectively moving the valve 50incrementally within the valve chamber 48 from the open position to theclosed position. The solenoid 56 can be in electrical communication withthe system controller 44, which drives the solenoid 56. Accordingly, thesystem controller 44 can communicate with the control valve assembly 42such that the valve 50 selectively closes and opens the first fluidpassage 52 and the second fluid passage 54, thereby dividing fluid flowproportionally therebetween.

As the valve 50 divides the flow of hydraulic fluid between the firstfluid passage 52 and the second fluid passage 54, the fluid can becorrespondingly directed to the motor supply conduit 36 b and the bypassconduit 40, respectively. Fluid directed to the motor supply conduit 36b may be supplied to, and discharged by, the motor 26 for powering theauxiliary power source 32 before returning to the pump 16 via the returnconduit 38. Fluid directed to the bypass conduit 40 can bypass the motor26 completely as it is steered immediately to the return conduit 38,without being supplied to the motor 26, for restoring to the pump 16.

Optionally, the hydraulic circuit 12 may include a fluid reservoir 58and a pump case drain 60 disposed at the pump 16, a motor case drain 62disposed at the motor 26, or both. The fluid reservoir 58 can be influid communication with the fluid circuit 22 and maintains hydraulicfluid on reserve that can be introduced to the pump 16 via the returnconduit 38. In an embodiment of the present invention, possible casedrain flow from the pump 16 and the motor 26 can be directed back to thefluid reservoir 58 through drain conduits 64 a-b (as illustrated in FIG.3). Fluid flow in the return conduit 38 can be directed through aventuri boost 66, where fluid from the fluid reservoir 58 may be drawninto the return conduit 38 to replace that lost from the case drainflow, and supplied back to the pump 16. Alternatively, the drainconduits 64 a-b can be disposed in the fluid circuit 22 such that casedrain flow can be pulled directly to the return conduit 38 by theventuri boost 66, without first being directed to the fluid reservoir 58(as shown in FIG. 1).

Additionally, the hydraulic circuit 12 may also include a fluid filter68 and a fluid cooler 70. The fluid filter 68 and the fluid cooler 70are preferably disposed serially with respect to the return conduit 38.However, it is to be understood that the fluid filter 68 and fluidcooler 70 can be disposed anywhere within the fluid circuit 22 withoutdeparting from the scope of the present invention. Impurities introducedinto the hydraulic fluid as it gets cycled through the fluid circuit 22can be filtered by the fluid filter 68. The fluid cooler 70, on theother hand, can cool fluid that passes therethrough. Accordingly, thefluid cooler 70 may include a heat exchanger (not separately shown) fordissipating heat to ambient air, an electrically operated fan 72disposed adjacent the heat exchanger for forcing ambient air through theheat exchanger, and a thermostat 74 (not separately shown in FIG. 1)which controls fan operation when fluid contained within the fluidcooler 70 exceeds a predetermined temperature. The thermostat 74 candirectly control the fan 72, or, alternatively, the thermostat 74 cancontrol fan operation through the system controller 44. For example, thethermostat 74 and the fan 72 may be in electrical communication with thesystem controller 44. The system controller 44 may receive temperaturereadings of the fluid in the fluid cooler 70 from the thermostat 74.Correspondingly, the system controller 44 can operate the fan 72 bytransmitting a fan control signal 76 to the fan 72 when fluid containedwithin the fluid cooler 70 exceeds the predetermined temperature.

The system 10, according to an aspect of the present invention, may alsoinclude a pressure sensor 78 a, a temperature sensor 78 b, a fluid levelsensor 78 c, an electrical output 78 d (FIG. 2 only), and a speed sensor78 d, collectively referred to as system control sensors 78. Each of thecontrol sensors 78 can be provided as part of the control circuit 14,shown in FIG. 2, and are configured to provide control inputs to thesystem controller 44. The control sensors 78 can be deployed throughoutthe system 10 to measure system vitals and assure the auxiliary powersource 32 is driven at constant speeds.

Referring back to FIG. 1, the pressure sensor 78 a can be disposed alongthe valve supply conduit 36 a proximate the pump 16 to sense hydraulicpressure. However, it is to be understood that there are many otherlocations in the fluid circuit 22 for positioning the pressure sensor 78a so long as it can accurately sense that the pump 16 is operating.Similarly, the temperature sensor 78 b can be disposed along the fluidcircuit 22 to monitor hydraulic fluid temperature. The temperaturesensor 78 b can be separate from the thermostat 74 and thus provideseparate input to the system controller 44, or, alternatively, thetemperature sensor can be the same as the thermostat. The fluid levelsensor 78 c can be disposed within the fluid reservoir 58 to monitor thelevel of hydraulic fluid within the reservoir 58. If the fluid levelbecomes low, the system controller 44 may announce a tell-tale alarm tothe operator. If the fluid level becomes extremely low, the systemcontroller 44 may cause the system 10 to shut down entirely to preventdamage to the pump 16.

In an embodiment of the present invention, the auxiliary power source 32can be an AC generator. Accordingly, the electrical output 78 d can be acurrent sensor, voltage sensor, or both for monitoring the generator'soperating characteristics, including current, voltage and frequency. Theelectrical output 78 d can be connected to output conductors 80 of thegenerator to sense the generator operating parameters. Alternatively,the speed sensor 78 d may be provided to monitor rotational speed of themotor 26 and the shaft 34, by sensing each revolution of the shaft 34,in order to provide controlled input to the system controller 44relating to operation of the hydraulic motor 26.

Referring now to FIG. 2, the control circuit 14 will be described infurther detail with reference to an AC generator as the driven auxiliarypower source 32, although other applications referred to in the detaileddescription are also possible. As previously described, the controlcircuit 14 may include the system controller 44 and one or more of thecontrol sensors 78, as well as a reference signal generator 82. Thesystem controller 44 can be a programmable controller having amicroprocessor (not separately shown) that implements control algorithmsfor the control of the generator output, namely voltage and frequency.The system controller 44 controls the generator output by applying acontrol output signal 84 to the proportional control valve assembly 42,directing the valve assembly 42 to meter fluid, and hence power, to themotor 26 for driving the generator. The system controller 44 varies thepower supplied to the hydraulic motor 26 through the use of the controloutput signal 84. Accordingly, the control output signal 84 can be apulse-width modulated voltage waveform or a variable DC output voltageapplied to the solenoid 56 of the valve assembly 42.

Vehicles today often rely on sensitive and delicate electronicsequipment, wherein only the cleanest of power is acceptable foroperation. Very little variance in the output frequency of an ACgenerator is tolerable in order to operate various devices such ascomputers and communications equipment. Merely close frequency output inrelation to desired frequency output is not good enough. Accordingly, itmay be desirable to compare actually frequency with a predeterminedfrequency, rather than merely relying on sensed motor speed as anindirect method of determining the generator's output characteristics.Of course, it is to be understood that sensing rotational speed of themotor 26 may be adequate in certain applications. Nonetheless, in anembodiment of the present invention, the electrical output 78 d can beelectrically coupled to the generator. The reference signal generator 82can be in electrical communication with the system controller 44 andgenerates a reference signal 86 indicative of the predetermined outputfrequency. The system controller 44 may include a comparing subcircuit88 that implements control algorithms for comparing sensed outputfrequency with the reference signal 86. The comparing subcircuit 88 canthen generate and transmit control output signals for controlling thevalve assembly 42 such that the supply of fluid conducted to the motor26 be sufficient to maintain desired generator output frequency.

The system controller 44, constructed in accordance with an exemplaryembodiment of the present invention, may also implement additionalcontrol algorithms for the electrical or mechanical system's outputfunctions in response to load variations, physical changes in theelectrical or mechanical system's operating environment or equipment,and communications from the user or other electronic modules. As theload on the electrical or mechanical system is increased or decreased,or the hydraulic fluid viscosity changes due to temperature fluctuationsand such, or the operating characteristics of the pump 16, motor 26, orthe valve assembly 42 change due to ambient conditions or wear, thesystem controller 44 can further adjust outputs to maintain consistentoperation of the electrical or mechanical system.

The control circuit 14 may further include an operator interface module90 enabling an operator of the system 10 to communicate with the systemcontroller 44 through a bi-directional asynchronous serialcommunications interface. The interface module 90 can display systemoperating parameters through an information display 92. As non-limitingexamples, the operating parameters displayed may include output voltage,frequency, current, hydraulic fluid temperature, total operating hours,and the like. The interface module 90 can also display or announce alarmconditions or faults detected by the system controller 44 and permit theoperator to interact with the system controller 44 and influence theoperation of the auxiliary power source 32. The alarm conditions can beannounced by an audible alert 94 included in the interface module 90.The operator may also influence the configuration of the systemcontroller 44. For example, the operator may turn the hydraulicallypowered system 10 on or off through an ON/OFF switch 96. Moreover, theoperator may configure the system controller 44 to automatically turnthe auxiliary power source 32 on when sufficient hydraulic pressure isdetected. Further, the operator can instruct the system controller 44 topurge air from the hydraulic lines, and configure the maximum expectedoutput values to be controlled by the system. The operator communicateswith the system controller 44 through a keypad 98 disposed in theinterface module 90. Furthermore, multiple interface modules may belinked together to add multiple operator interfaces if desired.

When the electrical or mechanical system to be driven is idle or shutdown, the valve 50 can be normally fully open, directing all fluid flowinto the bypass conduit 40, and depriving the motor 26 of power. At theoperator's request through the interface module 90, power can be meteredto the motor 26 by incrementally closing the valve 50, which beginsdiverting some proportional amount of fluid flow to the motor 26. Themore the valve 50 is closed, the more power can be provided to the motor26, thereby activating the electrical or mechanical system.

Alternatively, the application of hydraulic pressure to the fluidcircuit 22 may be interpreted by the system controller 44 as a commandto commence electrical or mechanical system operation. The operator maywish to configure the system controller 44 to automatically power theauxiliary power source 32 when the pump 16 is operating. If pressuresufficient for system operation is detected by the pressure sensor 78 a,system operation can automatically commence without further instructionfrom the operator. On the other hand, if the hydraulic pressure fallsbelow that required for system operation, the system controller 44 candirect the proportional valve 50 to open fully, diverting all fluid flowinto the bypass conduit 40, thereby shutting down motor operation.

The system controller 44 may further include a fluid pre-heatingsubcircuit 100. If the temperature sensor 78 b detects that hydraulicfluid in the system 10 is too cold for normal operation, the systemcontroller 44 can implement the fluid pre-heating subcircuit 100 to warmthe fluid to a safe operating temperature. The fluid pre-heatingsubcircuit 100 can generate control output signals for controlling theproportional valve assembly 42 such that fluid bypasses the hydraulicmotor 26 entirely until safe fluid operating temperature is obtained,avoiding damage to the mechanical components. The system controller 44can hold the proportional valve 50 fully open to circulate the hydraulicfluid through the bypass conduit 40. Normal mechanical friction willwarm the fluid until it reaches a first predetermined temperature, atwhich point the proportional valve 50 can be opened only enough to passthe warming fluid slowly through the motor 26. Normal mechanicalfriction will warm the fluid further until it reaches a secondpredetermined temperature, at which point full power operation cancommence.

The application of the fluid pre-heating subcircuit 100 can beincredibly advantageous in extremely low temperatures where thehydraulic fluid can partially congeal. If fluid were permitted to passthrough the motor 26 immediately, prior to frictional warming throughthe bypass conduit 40, lumps of congealed fluid can momentarily obstructthe motor gears causing the motor 26 to briefly decelerate and thenaccelerate. The deceleration and acceleration caused by lumps in thefluid passing through the motor gears occurs almost instantaneously,resulting in large voltage spikes at the output of the auxiliary powersource 32 (in the case of a generator). The duration of the voltagespike is very abrupt and the magnitude of the voltage spike can besufficient to damage various electrical loads. The fluid pre-heatsubcircuit 100 substantially minimizes this occurrence reducing warrantyclaims and the costs associated with, while greatly increasing customersatisfaction and good will.

Once pressure and temperature are sufficient, full system operation canbegin. In order to bring the system 10 up to power, the systemcontroller 44 may utilize a power ramping subcircuit 102. The powerramping subcircuit 102 can enable the system controller 44 to slowlyclose the proportional valve 50 so as to gradually apply power to thehydraulic motor 26. This gradual application of power allows the system10 to gently overcome inertial effects, greatly reducing wear andincreasing system component lifetimes.

With reference now to FIG. 4, a graphical representation of cold startoperation parameters of the system, utilizing the fluid pre-heatingsubcircuit 100 and the power ramping subcircuit 102, is illustrated.Pump speed 101 generally depicts revolutions per minute (RPMs) of thehydraulic pump 16 over time at initial system cold temperature start-up.Pump speed 101 can fluctuate over time as the vehicle engine speedfluctuates. Fluid temperature 103 generally depicts temperature of thefluid in the fluid circuit 22 during cold start operation. At coldstart, hydraulic fluid can bypass the motor 26 until it warms to asufficient temperature, at which point fluid is slowly diverted to themotor 26 to gradually supply power to the system. During this ramp-up,fluid temperature 103 can increase further permitting full systemoperation to begin. Motor speed 105 generally depicts operation of themotor (in RPMs) during cold start. The motor 26 can get little or nopower, while the fluid warms as it circulates through the bypass conduit40. Once a desired temperature is obtained, motor speed 105 ramps up asfluid is gradually supplied to the motor 26. Once full system operationcommences, motor speed 105 remains substantially constant, despitefluctuations in engine speed and hence pump speed 101.

Further, the system controller 44 may include an overtemperatureshut-down subcircuit. When the temperature of the hydraulic fluidexceeds safe operating conditions, the overtemperature shut-downsubcircuit 104 can notify the operator of the electrical or mechanicalsystem that excessive temperatures are being detected, and action may berequired to prevent damage to the system 10. When the temperatureexceeds yet another temperature threshold, the overtemperature shut-down subcircuit 104 can start an internal timer. If the timer expires,the proportional valve 50 may be fully opened by the overtemperatureshut-down subcircuit 104, bypassing all fluid flow and shutting down thehydraulic system 10 unless the operator issues an emergency overrideinstruction through the keypad 98 to prevent the shutdown and keep theelectrical or mechanical system operating.

The system controller 44 may also have the ability to record allabnormal conditions and faults to a diagnostic memory 106. The faultscan be retrieved from the diagnostic memory 106 by the operator anddisplayed by the interface module 90 to evaluate the conditions seen bythe system 10 and assist in any necessary troubleshooting. Recordedconditions may include, but are not limited to, valve voltage faults,valve current faults, over current faults, current sensing faults,temperature sensing faults, ground faults, number of over temperatureoverrides, fan faults, voltage sensing faults, hours run with overtemperature, highest recorded frequency, highest recorded voltage,highest measured current, highest measured temperature, hours run withovercurrent, hours on oil filter, calibration values, maximum currentvalues, and total hours.

Yet another advantage of the hydraulic control system 10, according tothe present invention is that it can be a self-contained system that canalso be readily retrofit to a vehicle having a power take of, enginedriven belt drive, or any other power supply source. Moreover, thesystem 10 may include a circuit breaker 108 as yet another protectivefeature. The circuit breaker 108 may be located in series with outputconductors 80 connected to output terminals of the generator. Thecircuit breaker 108 can operate conventionally by opening an externalcircuit (not shown), which is connected to the conductors to conductelectrical power to powered equipment.

A general overview of the operation of the hydraulic system electroniccontrol, according to a certain embodiment of the present invention, isprovided below. The system controller 44 can sense adequate operatingpressure in the fluid circuit 22. If the system controller 44 does notautomatically interpret sufficient pressure as a command to commenceoperation, it can wait to receive a command signal from an input,operator, or other electronic module to activate the hydraulicallypowered mechanical or electrical system. The system controller 44 canthen check the status and values of the control inputs to ensureoperation will be safe and effective. If the hydraulic fluid temperatureis too low, the fluid pre- heat subcircuit 100 can cause the fluid towarm to safe operating temperatures. The system controller 44 can thengradually apply power to the hydraulic motor 26 by slowly closing theproportional valve 50, according to the power ramping subcircuit 102.Appropriate control signals can be applied by the system controller 44to outputs in response to the control inputs to achieve the desiredcontrol and function of the system 10. If the hydraulic fluidtemperature becomes too high for safe operation, the overtemperatureshut-down subcircuit 104 can be implemented to shut down the operationof the electrical or mechanical system. The system's operatingparameters may be sent via serial communications using a proprietaryprotocol to the operator interface module 90 or other electronic module.If a command is received from the operator or other electronic module tocease operation, or the hydraulic pressure falls below that required foroperation, the system controller 44 can shut down the electrical ormechanical system by fully opening the proportional valve 50, bypassingall hydraulic fluid flow to the motor 26.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A hydraulic control system for driving an auxiliary power source,located aboard a motor vehicle having a primary power source, atconstant speed despite fluctuations in rotational speed of the primarypower source, the system comprising: a hydraulic pump drivablyconnectable to the primary power source, the hydraulic pump having aninlet for receiving fluid for pumping and an outlet for dischargingpumped fluid under pressure; a hydraulic motor drivably connectable tothe auxiliary power source, the hydraulic motor having an inlet forreceiving fluid under pressure and an outlet for discharging spentfluid; a fluid circuit including a supply conduit for conducting fluiddischarged by the pump to the motor, a return conduit for returningfluid discharged by the motor to the pump, and a bypass conduit forconducting fluid discharged by the pump directly to the return conduit,bypassing the motor, and returning fluid to the pump; a proportionalcontrol valve assembly disposed serially with respect to the supplyconduit and interposed between the outlet of the pump and the inlet ofthe motor, the control valve assembly having a housing including a valvechamber, a valve disposed within the valve chamber for apportioning theflow of fluid between the supply conduit and the bypass conduit, asolenoid drivably connectable to the valve for selectively moving thevalve incrementally within the valve chamber from an open position to aclosed position, a first fluid passage in fluid communication with thevalve chamber and the supply conduit going to the motor, a second fluidpassage in fluid communication with the valve chamber and the bypassconduit, wherein the valve selectively closes and opens the first fluidpassage and the second fluid passage proportionally dividing the flow offluid therebetween; and a control circuit in electrical communicationwith the valve assembly for controlling the valve assembly and hence thefluid flow within the first fluid passage to the motor supply conduitand the second fluid passage to the bypass conduit.
 2. The systemaccording to claim 1, wherein the control circuit comprises: anelectrical output sensor electrically coupled to the auxiliary powersource for determining output frequency of the auxiliary power source; areference signal generator for generating a reference signal indicativeof a predetermined output frequency; and a comparing subcircuit forcomparing sensed output frequency with the reference signal, and forgenerating a control signal controlling the valve assembly such that thesupply of fluid conducted to the supply conduit be sufficient tomaintain desired output frequency.
 3. The system according to claim 1,wherein the control circuit comprises: a speed sensor for determiningrotational speed of the hydraulic motor; a reference signal generatorfor generating a reference signal indicative of a predetermined rate ofrotation; and a comparing subcircuit for comparing sensed rotationalspeed of the motor with the reference signal, and for generating acontrol signal controlling the valve assembly such that the supply offluid conducted to the supply conduit be sufficient to maintain desiredrotational speed.
 4. The system according to claim 1, wherein thecontrol valve assembly is an electro-hydraulic servo control valveassembly.
 5. The system according to claim 1, wherein the controlcircuit further comprises a pressure sensor for determining sufficienthydraulic pressure for system operation, the pressure sensor causessystem operation to begin when hydraulic pressure is sufficient andcauses system operation to shut down when hydraulic pressure isdeficient.
 6. The system according to claim 1, wherein the controlcircuit comprises: a temperature sensor disposed in the fluid circuitfor sensing hydraulic fluid temperature; and a system controller havinga fluid pre-heating subcircuit for generating a control signalcontrolling the valve assembly such that fluid bypasses the hydraulicmotor entirely until safe fluid temperature is obtained.
 7. The systemaccording to claim 6, wherein the system controller further comprises apower ramping subcircuit for generating a control signal controlling thevalve assembly when sufficient fluid temperature is obtained such thatpower is supplied gradually to the hydraulic motor.
 8. The systemaccording to claim 6, wherein the system controller further comprises anovertemperature shutdown subcircuit for generating a control signalcontrolling the valve assembly when fluid temperature becomes too hotfor safe operation such that fluid bypasses the hydraulic motor,shutting down the auxiliary power source.
 9. The system according toclaim 8, wherein the control circuit further comprises an emergencyoverride accessible by an operator for instructing the system controllerto continue system operation when unsafe operating conditions exist. 10.The system according to claim 1, further comprising an interface modulehaving a display in electrical communication with the control circuitfor displaying real time system operating characteristics to anoperator.
 11. The system according to claim 10, further comprisingdiagnostic memory that records abnormal operating conditions and faultsfor subsequent retrieval by the operator through the display.
 12. Thesystem according to claim 10, wherein fault or alarm conditions aredisplayed by the interface module.
 13. The system according to claim 1,wherein the control circuit comprises a fluid level sensor disposed in afluid reservoir for generating a fluid level fault when the fluid levelfalls below a first minimum fluid level and a control signal shuttingdown the system when the fluid level falls below a second minimum level.14. The system according to claim 1, wherein the fluid circuit furtherincludes a hydraulic fluid filter disposed serially with respect to thereturn conduit.
 15. The system according to claim 1, wherein the fluidcircuit further includes a hydraulic fluid cooler disposed serially withrespect to the return conduit, an electrically operated fan disposedadjacent the hydraulic fluid cooler to pass ambient air through thehydraulic fluid cooler, and a thermostat disposed proximate thehydraulic fluid cooler to operate the fan when fluid contained withinthe hydraulic fluid cooler attains temperatures exceeding apredetermined temperature.
 16. The system according to claim 15, whereinthe fluid circuit further includes a hydraulic fluid filter disposedserially with respect to the return conduit, and a housing enclosing thehydraulic motor, the control valve assembly, the fluid filter, the fluidcooler, and a fluid reservoir, wherein the hydraulic motor, the controlvalve assembly, the fluid filter, the fluid cooler, and the fluidreservoir are readily installed as a unit on the chassis of a motorvehicle.
 17. The system according to claim 1, wherein the auxiliarypower source is a generator.
 18. The system according to claim 17,wherein the generator has output conductors and a circuit breaker foropening a circuit connected to the output conductors.
 19. The systemaccording to claim 1, wherein the fluid circuit further comprises afluid reservoir and a venturi boost for drawing fluid from the fluidreservoir into the fluid circuit.